Embodiments of the inventive concept relate generally to electronic memory technologies. More particularly, embodiments of the inventive concept relate to nonvolatile memory devices and related read methods.
Nonvolatile memory devices have been adopted for long-term data storage in a wide variety of technologies, such as mobile phones, digital cameras, personal digital assistants (PDAs), mobile computers, desktop computers, and various others.
One popular type of nonvolatile memory device is a flash memory device. In a flash memory device, data is stored in a cell transistor by modifying its threshold voltage. For example, in a single-level cell flash memory device, a bit of data is stored in a cell transistor by modifying its threshold voltage between an erased state and a programmed state.
In general, the threshold voltage of a flash cell transistor is determined by a number of electrons stored in a floating gate of the flash cell transistor. As more electrons are stored in the floating gate, the threshold voltage of the cell transistor increases. Unfortunately, the floating gate of a cell transistor can lose stored electrons over time, which can lower the cell transistor's threshold voltage. As the floating gate loses stored electrons, the reliability of the cell transistor tends to decrease.